Highly soluble stevia sweetener

ABSTRACT

A method for making a highly soluble Stevia sweetener is described. The resulting sweetener readily provides solutions with up to or greater than 30% concentration which are stable for more than 24 hours.

FIELD OF THE INVENTION

The invention relates to a process for the preparation of highly solubleindividual or combined sweet glycosides from a Stevia rebaudiana Bertoniplant extract, and more particularly for preparation of highly solublerebaudioside A.

DESCRIPTION OF THE RELATED ART

It is well known that Rebaudioside A exhibits so called polymorphism(Zell et al., 2000). Rebaudioside A amorphous, anhydrous and solvateforms differ significantly from each other in terms of solubility whichis one of the main criteria for the commercial viability of a sweetener.In this regard, as shown in Table 1, the hydrate form of Rebaudioside Adisplays the lowest solubility (Prakash et al., 2008). It was shown thatRebaudioside A may transform from one polymorph form to another atcertain conditions (U.S. pat. appl. Ser. No. 11/556,049).

TABLE 1 Properties of Rebaudioside A forms (US Pat. Appl. 11/556,049)Polymorph Forms Form 1 Form 2 Form 4 Hydrate Anhydrous Form 3 SolvateAmorphous Rate of Very low Intermediate High (>30% in High (>35% indissolution (<0.2% in 60 (<30% in 5 5 minutes) 5 minutes) in H₂Ominutes) minutes) at 25° C. Alcohol <0.5% <1% 1-3% <0.05% contentMoisture   >5% <1%  <3%  6.74% content

Patent application WO/2010/118218 describes a process of producinghighly soluble rebaudioside A by preparing a highly soluble hydratedcrystalline form. However the described methodology utilizes lowthroughput techniques such as evaporative crystallization or hotfiltration/centrifugation of slurries which can be hard to accomplish inlarge industrial scale.

On the other hand it is known (Prakash et al., 2008) that rebaudioside Aamorphous forms prepared by spray drying display high solubility aswell. However spray drying of rebaudioside A is a very challenging andlow throughput task because generally spray drying requires concentratedfeed solutions (about 50% solids content). Rebaudioside A concentratedsolutions prepared by simple dissolution are very unstable and tend tocrystallize very fast. These concentrated solutions (>10%) prepared bycommon solubilization methods such as heating under normal conditionscrystallize shortly after cooling down to room temperature. Thus spraydrying of such solutions requires special equipment capable ofmaintaining the solution at elevated temperature.

On the other hand extended exposure of rebaudioside A to hightemperature both in solid form and in aqueous solutions results inhydrolytic decomposition of the material (Prakash et al., 2008).

Therefore a high throughput process of manufacturing highly solubleRebaudioside A or other steviol glycosides on an industrial scalewithout needing a sophisticated equipment setup will offer certainadvantages compared to other techniques known to art.

SUMMARY OF THE INVENTION

The invention is directed to a method for producing a sweetenercomprising the steps of providing a Stevia sweetener powder andsolubilizing it in the water under gradient temperature treatmentconditions, to produce a highly stable concentrated solution, and spraydrying the highly stable concentrated solution to obtain a highlysoluble Stevia sweetener powder.

Hereinafter the term “steviol glycoside(s)” will mean Rebaudioside A,Rebaudioside B, Rebaudioside C, Rebaudioside D, Rebaudioside E,Rebaudioside F, Stevioside, Steviolbioside, Dulcoside A, Rubusoside, orother glycoside of steviol and combinations thereof.

Hereinafter, unless specified otherwise, the solubility of material isdetermined in RO (reverse osmosis) water at room temperature. Where thesolubility is expressed as “%” it to be understood as number of grams ofmaterial soluble in 100 grams of solvent.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory and areintended to provide further explanation of the invention as claimed.

DETAILED DESCRIPTION OF THE INVENTION

A process for the preparation of highly soluble Stevia sweetener,particularly Rebaudioside A, is described herein.

Crystalline Rebaudioside A has an inherently very low solubility,ranging from about 1%-2%. As described above, Rebaudioside A exhibitspolymorphism, resulting in a variety of forms with very differentcharacteristics and handling properties. The hydrate form has very lowsolubility (less than 0.2%), and is therefore not commercially viable asa sweetener. The solvate form has a solubility typically greater than30%, but this form has only of scientific interest and cannot be usedfor food or beverage applications because the level of residual alcohol(1-3%) makes it unfit for use in foods and beverages. The anhydrous formhas a solubility reported in literature of a maximum of up to about 30%solubility. The amorphous form has as solubility generally greater than30%, but for its preparation, the crystalline form has to be dissolvedin the water at very high concentrations (approx. 50%) which is notachievable by common solubilization techniques.

Typical spray drying techniques involve the use of a highlyconcentrated, and yet stable, starting solution to achieve the highestoutput possible. As noted above, crystalline Rebaudioside A has a verylow solubility, so to create a stable solution (one which will notcrystallize at room temperature), the solution has to be very dilute.Spray drying very dilute solutions is not economically efficient as theoutput of the spray dried powder will be very low. The need exists,therefore, for a process in which a high solubility Rebaudioside A isobtained by a process which does not require significantly dilutedRebaudioside A solution in order for the solution to be stable at roomtemperature.

In one embodiment of the present invention, an initial material,comprising sweet glycoside(s) of the Stevia rebaudiana Bertoni plantextract, which includes Stevioside, Rebaudioside A, Rebaudioside B,Rebaudioside C, Rebaudioside D, Rebaudioside E, Rebaudioside F,Steviolbioside, Dulcoside A, Rubusoside or other glycoside of stevioland combinations thereof, was combined with water at a ratio of about1:1 (w/w).

The obtained mixture was further subjected to a gradient heat treatmentwhich resulted in high stability and high concentration solution. Thegradient of about 1° C. per minute was used in heating the mixture. Themixture was heated to the temperature of about 110-140° C., preferablyabout 118-125° C. and was held at maximum temperature for about 0-120min, preferably about 50-70 min.

After the heat treatment the solution was cooled down to roomtemperature at gradient of about 1° C. per minute. 24-hour incubation ofthis high stability and high concentration solution did not show anycrystallization.

The solution was spray dried by a laboratory spray drier operating atabout 175° C. inlet temperature and about 100° C. outlet temperature. Ahighly soluble amorphous form of rebaudioside A was obtained withgreater than about 30% solubility in water at room temperature.

The following examples illustrate preferred embodiments of theinvention. It will be understood that the invention is not limited tothe materials, proportions, conditions and procedures set forth in theexamples, which are only illustrative.

EXAMPLE 1 Preparation of Rebaudioside A Concentrated Solution

100 g of rebaudioside A containing Stevioside 0.2%, Rebaudioside C 0.3%,Rebaudioside F 0.3%, Rebaudioside A 97.7%, Rebaudioside D 1.0%, andRebaudioside B 0.3%, all percentages being on a percent dry weightbasis, and having water solubility of 0.6% was mixed with 100 g of waterand boiled on a laboratory heater until complete dissolution. Uponcomplete dissolution, the solution was cooled to room temperature tomake Solution #1.

EXAMPLE 2 Preparation of Rebaudioside A Concentrated Solution

100 g of rebaudioside A containing Stevioside 0.2%, Rebaudioside C 0.3%,Rebaudioside F 0.3%, Rebaudioside A 97.7%, Rebaudioside D 1.0%,Rebaudioside B 0.3%, all percentages being on a percent dry weightbasis, and having water solubility of 0.6% was mixed with 100 g of waterand incubated in autoclave (AMA 270, Astell Scientific, UK), at 121° C.for 1 hour. Upon completion of incubation period the obtained clearsolution was cooled to room temperature to make Solution #2.

EXAMPLE 3 Preparation of Rebaudioside A Concentrated Solution

100 g of rebaudioside A containing Stevioside 0.2%, Rebaudioside C 0.3%,Rebaudioside F 0.3%, Rebaudioside A 97.7%, Rebaudioside D 1.0%,Rebaudioside B 0.3%, all percentages being on a percent dry weightbasis, and having water solubility of 0.6% was mixed with 100 g of waterand incubated in thermostatted oil bath. The temperature was increasedat 1° C. per minute to 121° C. The mixture was maintained at 121° C. for1 hour and then the temperature was decreased to room temperature (25°C.) at 1° C. per minute to make Solution #3.

EXAMPLE 4 Rebaudioside A Concentrated Solution Stability

Rebaudioside A Solution #1, Solution #2 and Solution #3 preparedaccording to EXAMPLE 1, EXAMPLE 2 and EXAMPLE 3, respectively, wereassessed in terms of their stability at room temperature (25° C.). Theresults are summarized in Table 2.

TABLE 2 Rebaudioside A concentrated solution stability (50% totalsolids, 25° C.) Time, Observation hrs Solution #1 Solution #2 Solution#3 0.5 Clear solution Clear solution Clear solution 1 Intensive Cloudysolution, precipitate Clear solution crystallization on the bottom 2Viscous slurry Intensive crystallization Clear solution of crystals 4Solidified Viscous slurry of crystals Clear solution crystalline mixture24 Solidified Solidified crystalline mixture Clear solution crystallinemixture

It can be seen that the solution prepared by temperature gradient methodshows greater stability against crystallization.

EXAMPLE 5 Preparation of Highly Soluble Rebaudioside A

Rebaudioside A Solution #1, Solution #2 and Solution #3 preparedaccording to EXAMPLE 1, EXAMPLE 2 and EXAMPLE 3, respectively, weredried using YC-015 laboratory spray drier (Shanghai Pilotech Instrument& Equipment Co. Ltd., China) operating at 175° C. inlet and 100° C.outlet temperature. Solution #1 and Solution #2 had to be maintained at80° C. to prevent premature crystallization whereas Solution #3 wasmaintained at room temperature. The Solution #1 yielded Sample #1,Solution #2 yielded Sample #2 and Solution #3 yielded Sample #3.

The obtained amorphous powder samples were compared for solubility(Table 3).

TABLE 3 Highly soluble Rebaudioside A Solubility, Observation % Sample#1 Sample #2 Sample #3 5 Clear solution Clear solution Clear solution 10Slightly cloudy Clear solution Clear solution solution 20 Cloudysolution Slightly cloudy Clear solution solution 30 Undissolved matterCloudy solution Clear solution on the bottom 40 Significant amount ofSignificant Slightly cloudy undissolved matter amount of solutionundissolved matter

The process of the present invention resulted in a Rebaudioside Apolymorph which demonstrated high degree of solubility in water.Although the foregoing embodiments describe the use of Rebaudioside A,it is to be understood that any Stevia-based sweetener may be used andprepared in accordance with this invention, and all Stevia-basedsweeteners are contemplated to be within the scope of the presentinvention.

Although the invention and its advantages have been described in detail,it should be understood that various changes, substitutions andalterations can be made herein without departing from the spirit andscope of the invention as defined by the appended claims. Moreover, thescope of the application is not intended to be limited to the particularembodiments of the invention described in the specification. As one ofordinary skill in the art will readily appreciate from the disclosure ofthe invention, the compositions, processes, methods, and steps,presently existing or later to be developed that perform substantiallythe same function or achieve substantially the same result as thecorresponding embodiments described herein may be utilized according tothe invention.

1. A method for producing a highly soluble sweetener comprising thesteps of: A) providing a Stevia sweetener powder; B) providing a solventconsisting essentially of water; C) mixing the solvent water and Steviasweetener powder to make a mixture; D) increasing the temperature of themixture by a gradient heat treatment method having a rate of temperaturechange of about 1° C. per minute to an elevated temperature of about110-140° C. to make a solution; E) holding the solution at the elevatedtemperature; F) decreasing the temperature of the solution by a gradientcooling method having a regular rate of temperature change to obtain astable Stevia sweetener solution having a clear solution stabilitywithout visible crystallization or cloudiness at 25° C. for 24 hours;and G) optionally spray drying the stable Stevia sweetener solution, toprovide an amorphous highly soluble powder of Stevia sweetener having asolubility of at least about 5 grams per 100 grams of water. 2.(canceled)
 3. The method of claim 1 wherein Stevia sweetener is selectedfrom a group consisting of: Stevioside, Rebaudioside A, Rebaudioside B,Rebaudioside C, Rebaudioside D, Rebaudioside E, Rebaudioside F,Steviolbioside, Dulcoside A, Rubusoside, or other glycoside of steviol,and a mixture thereof.
 4. The method of claim 1 wherein the water andStevia sweetener powder ratio in the mixture is 1:1 (w/w).
 5. The methodof claim 1 wherein the decreasing of the temperature of the solution isat a gradient of about 1° C. per minute.
 6. The method of claim 1wherein the solution is held at 110-140° C. for about 50-70 minutes. 7.The method of claim 1 wherein the stable Stevia sweetener solution isspray dried on a spray drying apparatus operating at 175° C. inlet and100° C. outlet temperature.
 8. (canceled)
 9. A highly soluble sweetenermade by the method of claim 1, wherein the highly soluble sweetener hasa solubility of at least about 5 grams per 100 grams of water. 10.(canceled)
 11. The highly soluble sweetener of claim 9, having asolubility of at least about 40 grams per 100 grams of water.